The remains of an Iron-Age Dutch urn field (Free University of Amsterdam)
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Bad dirt is the reason behind a shift in burial practices in the southern Netherlands, according to Fokke Gerritsen, an archaeologist with the Free University of Amsterdam. Between 800 and 600 B.C., itinerant farmers built cemeteries containing hundreds of monumental mounds. "In one mound there was typically one cremation burial, usually in an urn, which became a symbol for a family," says Gerritsen, who notes that building the huge cemeteries, or urn fields, must have been a collective effort. By 500 B.C., however, the Iron Age population was digging humble graves in small plots near houses.

"During the period when the urn fields were in use, farmers frequently moved to new locations and the land around the burial mounds was held as common property," says Gerritsen, "People who shared burial sites saw themselves as a community, with common ancestors and common land, which distinguished them from other groups." But as fertile soil became scarcer, farmers began to hold on to individual fertile plots, cultivating the same piece of land and passing it down to the next generation. As the importance of the outside community faded, the social cohesion reinforced by the urn fields dissolved and the monumental cemeteries fell into disuse.